1. Field of the Invention
The present invention is related to an easy mode pipe-diameter reducing device, and especially to such a device of which the inner wall is made with an inner thread thereon to extend from a section with constant diameter to a tapered section, in order to be benefit to feeding of the pipe into the die cavity of the device. With the threaded tapering wall to give surrounding pressing function for reducing the pipe diameter, a straight pipe can be easily formed into a pipe with reduced diameter, and easiness of pipe reducing can be achieved.
2. Description of the Prior Art
The metallic pipes used in the present invention can be divided into two groups: low carbon steel alloy pipes (such as steel pipes) and softer pipes made of nonferrous alloy (such as copper alloy pipes, aluminum alloy pipes and titanium alloy pipes). These metallic pipes normally are used in common mechanical structural members or piping members as supporting pipes or conveyer tubes. The pipes can be molded to be used as metallic rail pipes, metallic chair frame pipes, bicycle frame pipes, artistic decoration pipes etc. However, in manufacturing pipes for the abovementioned purposes, the pipes have to be bent or reduced in diameter.
Among the processes in the art relative to the technique of diameter reducing into conical shaped pipes, the preferred method is the rotary swaging, which reduces diameters of the pipes by swaging them into conical pipes. However, rotary swaging is suitable only for processing the above mentioned low carbon steel alloy pipes.
In known pipe-diameter reducing techniques, a U.S. Pat. No. 1,919,254 discloses a steel die provided with a plurality of die plates to produce thread like undulated pipes; a U.S. Pat. No. 3,492,849 discloses a steel die to gradually reduce diameters of pipes, and the steel die is provided therein with a plurality of rolling beads arranged in the form of a spiral thread, the rolling beads can be rolled along the thread to practice a technique of rotary swaging for making a spiral pipe; and a U.S. Pat. No. 3,727,443 discloses a die for pipes provided in a die cavity thereof with a plurality of rolling beads, each rolling bead in a recess can be individually adjusted, so that the rolling beads can be controlled to adjust the amount (degree) of pipe reducing by rotary swaging, in this way, a reduced pipe with a smooth surface can be obtained. If it is used to process the softer pipes made of nonferrous alloy, the pipes being processed are compressed by the rolling beads; by virtue that the pipes made of nonferrous alloy has insufficient strength for forming, the stress generated therein can not be uniformly scattered, thereby, the walls of the pipes are subjected to having rough edges looking like an orange skin as a whole. Pipe walls after being reduced into conical shaped pipes are not typically smooth. The structural complexity of a rotary swager and the higher cost of the equipment cause rotary swaged pipes to be uneconomic.
Therefore, in order to work on the low carbon steel alloy pipes and the softer pipes made of nonferrous alloy on the same equipment for reducing diameters to get smooth and fine pipe walls, conventional rotary swaging techniques do not suffice. It is difficult to obtain smooth pipe walls without rough edges or seams by other forming technique in the art also. The easy mode pipe-diameter reducing device of the present invention suits metallic pipes of low carbon steel alloy and nonferrous alloy more widely, the device itself is made to be simple for working, and this is the motive of studying and developing the present invention.